The present invention relates generally to task chairs which dynamically support the body of the user in healthy positions while performing various tasks over extended seating periods.
In the past century, much of the industrialized world has dramatically changed. Inventions have altered the way work is performed. At the turn of the 20th century, work was more physical, active and erect. At the close of the 20th century, the average worker has less physical activity and the worker performs more of their work in a seated position.
Anatomical science teaches that if any part of anatomical function is impinged or static for periods of time, dysfunction (poor health) will result. Dysfunction restricts the ability to animate. Limited animation eventually leads to poor health. Good health will optimize performance and quality of life.
In the mid-1980s, new health problems became evident as industrial society was becoming more and more sedentary and good health was on the decline. Society was advised to become more active. Aerobics, jazzercise, weight training, various types of workouts and physical activities of all kinds were encouraged. Many working professionals responded and incorporated physical activity into their daily routine.
Yet while health improved for some, many others either chose not to incorporate physical activity in their schedule, or were unable to because of schedule restraints. With many in our society being both providers and caretakers of the family, opportunity for scheduled physical activity is limited.
People from both groups, those with physical activity and those without, were having similar health issues. A common denominator was determined to be seating doing tasks for long periods of time at work and/or at home. Many experienced lower back pain, muscle tension, numbness, acid reflux, carpel tunnel syndrome and general fatigue.
Peter Escogue, a recognized anatomical functionalist, suggests these problems are posture related as well as inactivity related. Proper anatomical posture promotes proper anatomical function, i.e. the body functions best when operated from a proper position. Escogue further observes that over a period of time, many have compromised their correct posture, therefore compromising correct function. The discomfort symptoms are the body's way of alerting us that function is impinged by an improper posture.
Static improper posture, while sitting in a static improper supporting chair, causes poor seating health. Originally sitting, especially chairs, were designed for two separate purposes:
A place to rest from activity. The erect active worker looked to sit (atop, rest, relax) in a comfort giving chair, like the Lazy Boy® recliner. A chair as a work device. Function, not comfort, was primary, like a stool.
Later, chair manufacturers saw the need for something different for the seated worker, thus, the creation of the task chair. The natural progression was to combine both into one. Work chairs got pads, tilts, swivels, etc. Over time, health improvements were added to the combination of the family room recliners and the worker's rigid elevating stool. Additions like lumbar supports, adjustable armrests, shaping of seat back to a general vertebrae contour, etc., were included.
Evolving task chairs combined elements from comfort chairs with a worker's stool. The addition of health features continually posed a compromise between comfort and the task. Today's combination task chairs offer few features to accommodate multiple tasks with little consideration for seating health.
Task chairs are typically configured to allow tilting of the seat and backrest as a unit or tilting of the backrest relative to the seat. In chairs having a backrest pivotally attached to a seat in a conventional manner, the movement of the backrest relative to the seat can create shear forces acting on the legs and back of the user. These shear forces tend to cause an uncomfortable pulling of the user's clothing. In an attempt to compensate for these shear forces, some office chairs include a backrest which pivots while the seat tilts, such as those disclosed in U.S. Pat. No. 2,859,801 (Moore) and U.S. Pat. No. 4,429,917 (Diffrient).
A related disadvantage of conventional task chairs is the configuration of the seat and/or backrest. Such seats typically include single or multi-density foam padding with a covering such as cloth, leather, mesh material or the like. Such seating also tends to provide insufficient aeration since it acts as another layer of clothing and does not contain a Spinal Relief Channel in the back support, and/or contain a Coccyx Relief in the horizontal seat. In addition, the structural requirements of such an attachment limits the shape and size of the frame and the membrane.
Typically, the seats of office task chairs are supported by a single stage telescoping column which provides for vertical adjustment of the seat. These columns include a gas spring mounted in a telescoping tube which is slidable within a base tube. In accordance with guidelines set by the American National Standards Institute (A.N.S.I.) and Business and Institutional Furniture Manufacturer's Association (B.I.F.M.A.), conventional office chairs in the United States are typically adjustable from a seat height of 16.0 inches from a floor to about 20.5 inches from a floor. Nevertheless, it is desirable to exceed this range of height adjustment to account for very small or large users and to accommodate the international population in general.
Typically, it is difficult to exceed this range of height adjustment with seats which tilt about the knees or ankles of the user. To offset the moments acting on single stage support columns, pneumatic manufacturers typically set a minimum overlapping distance of 2.95 inches (75 mm) between the tubes. Because such “ankle tilt” and “knee tilt” chairs have relatively large tilt housings, it is difficult to provide a lower minimum and higher maximum seat height while maintaining the required overlapping distance between the tubes. These types of tilting chairs also impart a greater moment on the tube since the pivot axis is offset from the support column. It is therefore desirable to provide a vertically adjustable support column having a greater overlapping distance to permit a greater stroke which decreases the minimum height and increases the maximum height of a chair seat.